A Serializer/Deserializer (SER/DES) is a pair of functional blocks [integrated circuits or IC/chip] commonly used in high speed communications. These blocks convert data between serial data and parallel interfaces in each direction. Although the term “SER/DES” is generic, in speech it is sometimes used as a more pronounceable synonym for Serial Gigabit Media Independent Interface (SGMII).
SER/DES chips facilitate the transmission of parallel data between two points over serial streams, reducing the number of data paths and thus, the number of connecting pins or wires required. Most SER/DES devices are capable of full duplex operation, meaning that data conversion can take place in both directions simultaneously. SER/DES chips are used in many application including Gigabit Ethernet systems, wireless network routers, fiber optic communications systems, storage applications just to name a few.
Specifications and speeds vary depending on the needs of the user and on the application. These blocks are often integrated within another Integrated Circuit (i.e. ASIC).
The quest for “smaller, cheaper, faster” devices is ever increasing. IC packaging is one area that this quest is continuously challenged. In IC packaging chips are mounted on and connected to a rigid laminate (substrate) via wirebonds (FIG. 1) or bumps in flip chip (FIG. 2) applications. FIG. 1 illustrates an IC packaging chip having a mold (101) and die attach material (105). In wirebond technology (FIG. 1) the silicon die (102) is connected via wires (108) to metal layer (106) over a rigid laminate (103). The metal layer (106) is then connected to solder balls (104) through Via holes (107) inside the rigid laminate (103). In flip chip technology (FIG. 2), the silicon die (201) is connected to a substrate (203) via balls (202) and the substrate (203) routes the metal to proper solder balls (204).
Packaging SER/DES is a very challenging and specialized area in the world of IC packaging. With higher data rate flip chips are adapted for packaging high speed SER/DES because in Flip Chip packaging wirebonds are replaced by conductive solder bumps thereby wirebond inductance is no longer present.
At the present, industry is moving toward 3D packaging where two or more dice are stacked on the top of each other or packages are stacked on the top of packages. These packaging methods offer high density integration in smaller footprint making it suitable for applications in which size matters such as cell phone. FIG. 3 is an example of two equal size chips placed vertically in the same package, in which the chips are connected to the solder balls (305) using wirebond technology. As can be seen from FIG. 3, a first die (301) is placed above a second dies (302), which in turn is placed above a substrate (306). A spacer (303) is placed between the two dies. Another spacer (304) is placed between the bottom die (302) and the substrate (306). FIG. 4 is another example of 3D chip stacking in which the SER/DES die (404) is not stacked and is positioned as a side die beside the stacked dice (401 and 403). FIG. 4 illustrates a stacked die packaging having spacer (402), die attach material (405 and 406), solder balls (407), a rigid laminate (substrate) (408), and via holes or vias (409).
The drawback of stacked die packaging is the use of wirebond, making it unsuitable for high speed SER/DES packaging. In order to circumvent this impediment, this invention proposes to use Through Silicon Via (TSV) to connect dice vertically.
The benefits of using TSV to connect dice vertically are:
1. Higher degree of miniaturization: By placing TSV within the SER/DES block one can facilitate the connection of the die above or below that would otherwise be placed side by side. In a case where non SER/DES dice are stacked with wirebond and SER/DES die is placed next to it, using TSV will eliminate all wires.
2. Placing TSV makes it possible to stack two or more dice with SER/DES block
3. Electrical superiority: When using TSV, it is possible to stack and connect very high data rate SER/DES blocks vertically without the need for any wire.
4. Better thermal performance: The TSV placed within the SER/DES block provides a highly conductive passage for heat removal from the die above.
5. No need for spacer material: Normally, thick Spacer materials are placed between the dice to make wire-bonding of same or different die size possible. Using TSV eliminates the need for this material thereby reducing the cost as well as decreasing the overall height of the package making it possible to fit the package in places where height is a constraint such as very thin cell phones.
This patent claims the placement of TSV within the SER/DES block to enable high density packaging of dice with SER/DES blocks or any other block.